Micro-CT evaluation of apical enlargement of molar root canals using rotary or reciprocating heat-treated NiTi instruments

Abstract

Micro-CT evaluation of apical enlargement of molar root canals using rotary or reciprocating heattreated NiTi instruments Objective: The aim of this study was to evaluate the root canal preparation and apical enlargement of molar root canals with rotary or reciprocating heat-treated nickel-titanium (NiTi) instruments, by using micro-computed tomography (micro-CT). Methodology: Mesial root canals (n=48) of mandibular molars, with a curvature between 20° and 40°, were prepared with ProDesign Logic (PDL) 25.01 and 25.06 in rotary motion, or ProDesign R (PDR) 25.06 in reciprocating motion (PDR). Apical enlargement was performed with PDL35.01 and PDL35.05 or PDR35.05. Scanning with 9 µm resolution was performed before and after preparation, and, after apical enlargement, by using micro-CT. The percentage of volume increase, debris and untouched root canal surface, transportation, centralization and preparation time were analyzed. ANOVA and Tukey or Kruskall-Wallis and Dunn statistical tests were conducted (α=.05). Results: PDL promoted a higher apical percentage of volume increase, and lower percentage of debris and untouched root canal surface than PDR 25.06 preparation in entire canal and in all thirds (P<.05). Apical enlargement with PDL 35.05 and PDR 35.05 produced a higher percentage of volume increase in the apical region in relation to the initial preparation (P<.05). PDR 35.05 and PDL 35.05 showed similar results in relation to percentage of debris and untouched root canal surface in entire canal and in all thirds (P>.05). Centralization and transportation showed no difference (P>.05). PDR required less time to perform preparation and apical enlargement (P<.05). Conclusions: The apical enlargement 35.05 with CM heat-treatment instruments using reciprocating and rotary motion reduced the percentage of debris and untouched root canal surface, without causing deviations or procedural errors. The protocol of greater apical enlargement favors the cleaning of the root canals in both kinematics. Preparation by the reciprocating system was faster than by the rotary system.

Influence of voxel size on micro-CT analysis of debris after root canal preparation

“…25 Micro-CT has been used in recent studies to evaluate debris accumulation, owing to its high accuracy and high spatial resolution. 2,5,6,7,8 The first null hypothesis was accepted, because similar results were observed for root debris, using different voxel size analyses.…”

“…Since then, micro-CT imaging has been used to evaluate debris accumulation. 5,6,7,8,9 However, micro-CT analysis can be influenced by many factors, such as different scan settings, image resolutions and ring artifacts. 10 Different Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.…”

“…10 Different Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript. micro-CT acquisition resolutions are used to analyze debris accumulation, using scanning voxel sizes of 9 µm, 5,7 14 µm 8,11 , 18 µm, 6,12 and up to 20 µm. 2 The different means of image acquisition and image evaluation make it difficult to discuss results and compare different studies.…”

“…New mechanized heat-treated nickel and titanium (NiTi) instruments have been proposed especially for centralized preparation in curved root canals. 5,14 ProDesign Logic (PDL) (Easy Equipamentos Odontológicos, Belo Horizonte, MG, Brazil) manufactures NiTi instruments submitted to a heat treatment and featuring a controlled memory (CM), with improved flexural resistance. 15 Hyflex EDM -HEDM (Coltène/Whaledent, Allstätten, Switzerland) also makes heat-treated CM instruments, and offers a surface treatment, called electro-discharge machining (EDM).…”

“…18 However, previous studies have observed large amounts of accumulated debris in root canals after preparation with mechanized NiTi instruments. 4,5,7 Final irrigation protocols, such as passive ultrasonic irrigation (PUI), have been proposed to improve the cleaning of root canals. 4,7 Irrisonic (Helse Ultrasonic, Santa Rosa de Viterbo, SP, Brazil) is an ultrasonic tip indicated for performing PUI.…”